Dylan Crandall is the putative biological father of a patient of House's whom House had gone to college with (most likely at Hopkins) when both had just turned twenty. House claimed that the only reason that they had been friends was that Crandall had a car. However, they did share an interest in music. House repeatedly shows scorn for Crandall's supposed gullibility and unwillingness to potentially poison his relationship with his new-found child by taking a paternity test. However, House also shows concern for him throughout the ordeal, and ultimately lies about the results of a paternity test he secretly administered, telling them that they are father and daughter despite the negative result, because he knows that that is what will make Crandall happy (or, perhaps, ensuring the patient is guilted into staying with him). Of course, this could also be guilt on House's part over the fact that he stole one of Crandall's girlfriends away from him in college, ostensibly to prove to Crandall that she was untrustworthy and potentially unstable.
Crandall is the only known person who uses a nickname (other than "Greg") for House, calling him "G-Man," and the only known person from whom House does not seem to mind this sort of behavior. This seems to indicate a deeper attachment for House than simple vehicular ownership would justify.
Crandall is one of very few former acquaintances of House who have appeared in the series. He is one of even fewer of the people House would consider a friend. Apart from House's parents, Crandall is probably the oldest friend of House's who has ever appeared on the series.